In the past couple of decades, Hydrogen has been studied as an intriguing potential energy vector in the Energy Transition. From consideration as an alternative fuel, for mid-term decarbonizing blending opportunities in existing infrastructure, in remote operation, to long term energy storage of excess renewables and grid stabilization, the initial hype has become a feet-on-the-ground attempt to determine where exactly Hydrogen can play a role in decarbonization pursuits within the energy and transportation sectors. Previous Darcy coverage down the Hydrogen value chain is logged in our Hydrogen Master Framework.

Hydrogen’s ability to store more energy per unit weight than other fuels, its potential to be produced by carbon neutral or carbon negative methods, as well as its possible end-uses are benefits often sited by those on the Hydrogen hype train. Unfortunately, this dream world of a perfect hydrogen economy fueling the energy transition doesn’t come without challenges.

Around 96% of hydrogen currently produced comes from carbon-based sources, and has significant emissions associated with its production without carbon capture. The color spectrum associated with hydrogen production technologies isn’t helping universal clarity in the emissions-related implications to various production technology choices. However, if existing hydrogen production can be replaced with carbon neutral or carbon negative methods, the potential for the molecule as an energy vector in the Energy Transition is intriguing.

Additional to the challenge of first decarbonizing existing production (with an ever expanding market) to see any real decarbonizing potential with hydrogen, “clean” hydrogen is often cost prohibitive.

But why?

Honestly, advances in production have reached a point at which one of the only things driving cost is lack of scale, due to lack of a market (for clean H₂), which is driven by cost…a vicious circle. Transportation and storage with traditional compressed gas methods is expensive, high volume, and requires many safety protocols and regulatory hurdles. Additionally, the low ambient temperature density of hydrogen results in a low energy per unit volume, requiring the development of advanced storage methods that have the potential for higher energy density. I’ll mention some of its other tricky chemical attributes later. Finally, supply and value chains in the space are complex and need development, and safety/regulatory standards and societal acceptance (think Hindenberg) could still use work.

Mastering hydrogen storage is key to enabling the advancement of other hydrogen and fuel cell technologies in applications including stationary or backup power, portable power, transportation, and energy storage at various scales, with markets ranging from remote operation to grid stabilization. Indeed, even beyond the production piece, without tackling storage and transport of this tricky molecule, we’re never going to meet our goal of making the molecule cost competitive, or seeing the hyped “green” hydrogen economy expand.

USE CASE: ENERGY STORAGE

Many are betting on hydrogen being a future solution for energy storage, as we move further and further into saturation with renewables. Seen on the framework below, you can see where hydrogen and chemical storage compares to some other alternatives in the energy storage space. It can be seen how all the technologies listed match the different energy storage categories according to their discharge time (y axis) and rated power (x axis.)

Hydrogen is a tricky chemical to manage, yes, but if we can tackle that engineering piece, it has the potential to not only serve a role in energy storage for applications like transportation, but also in transmission and distribution grid support as well as energy management, issues that are becoming more and more relevant as more renewables come into play in the grid, and as we further try to solve the energy scarcity issues throughout the world.

LET'S GET TECHNICAL…

Hydrogen can be stored with physical or material based storage, as can be seen in the clickable framework below. Recently we started our in-depth coverage of the hydrogen storage space with an event more focused on physical storage methods featuring Plug Power, speaking on both gaseous and liquid storage and various scales, and Shell, discussing their import/export scale liquid hydrogen project.

Hydrogen storage right now via physical methods is a tough nut to crack – the regulatory hurdles are a mess due to the necessary high pressure and flammability of the fuel, losses due to boil off historically have caused methods to die when considering economic viability, also the tendency of hydrogen, a fast little guy, to cause embrittlement of traditional materials by burrowing into them has caused the biggest cost piece to be in the requirement of very expensive materials and coatings to prevent this – as well as to take the temperature requirements. In compressed gas storage, currently the most common technique, you have to deal with high pressures of 5-10,000 bar, expensive materials, and densities that are still below the DOE goals, causing size/volume to be an issue. The infrastructure and supply chain, however, is the most developed.

If you look at this first orange bar in the middle of the framework, you’ll see a list of parameters for each storage technology, % hydrogen by mass, volumetric density, pressure, temperature of storage, and temperature or energy requirement for release. Very simply I have used green checks to mean - generally positive -, red x’s to mean - generally negative or difficult to manage -, and yellow circles to designate neutral, or when it varies too much per technology within the group to properly categorize. If you want to reference some general average data for each storage type, check out the comparison linked at the bottom of this framework.

Compressed Gas: Some of the biggest issues with hydrogen storage via compressed gas are the high pressure, as mentioned, the expensive materials required for the tanks, the safety concerns and regulatory issues, and the volume required to store a useful amount of hydrogen. Currently some leading companies working in the space are Air Liquide, NPROXX, and MAHYTEC.

Cryo/Cold Compressed Hydrogen: Cryo/Cold compressed hydrogen increases the density potential of the fuel, making it more financially viable where high density hydrogen storage is required under limited space, or where a larger roundtrip distance is involved. This method is difficult and energy intensive to maintain, with possible losses to boil off and an expensive infrastructure requirement, but for need cases that require high density and low volume, it can be considered. A couple of companies working in this space are Verne and Cryospain.

Liquid: As a liquid, due to the tricky chemistry of phase changes with the molecule – I mean the boiling point at atmospheric pressure is -252.8C – storage requires cryogenic temperatures. Liquid hydrogen has a much higher density and lower volume requirement than traditional storage, but there are efforts to be made in terms of storage scale (take a look at Shell’s presentation on some of the engineering hurdles they are facing with their import/export scale project), the energy intensive liquefaction process, tank engineering, and economics. Some companies working in this space are Plug Power and ZeroAvia, who we heard from at a previous forum on their work with liquid hydrogen for aviation applications.

More recent development has gone into material methods of hydrogen storage. Hydrogen can also be stored on the surfaces of solids via adsorption, through liquid organic hydrogen carriers, within solids, by absorption, chemically in molecules like ammonia, or, as is becoming quite prevalent in large scale projects announced recently, in salt caverns.

Physiadsorbtion: Storage based on physiadsorbtion provides a potentially higher energy efficiency than the rest of the mentioned storage options, given that the hydrogen is retained at a low temperature and 100% of the hydrogen adsorbed can be recovered. The low boiling point of hydrogen causes some technologies in this space to require very low temperatures to attain sufficient amounts of adsorbed hydrogen, but the release can be accomplished with very small changes of pressure and/or temperature, and with very rapid response. There are packing limitations, weak adsorption enthalpies, and the low temperature requirement is still an issue to consider, but some companies claim to have overcome this. One promising company working in this space is Hydrogen in Motion.

Liquid Organic Hydrogen Carriers: Liquid organic hydrogen carriers can function at higher densities and lower pressures than traditional storage, but suffer from expensive catalyst development, boil off issues, energy expense, and needs additional solvent research. However, companies in the space as well as research organizations are making strides. This method is mostly being considered for long distance transport, due to its similar properties to crude oil based liquids, allowing known processes to be adapted. An interesting company working in this space is Hydrogenious.

Interstitial Hydrides: Hydrogen can also be chemisorbed; in interstitial hydrides the hydrogen molecule essentially breaks and the Hydrogen atoms become a part of the crystal lattice of the material. This method retains the hydrogen without losses well for long periods of time, but suffers from low gravimetric density, slow/complex desorption kinetics, and has an energy requirement for hydrogen release. Many companies have commercialized this technology for niche applications; it's especially great for applications where there is waste heat that can be integrated for the hydrogen release stage, and, in fact, several companies are developing fully integrated storage systems for power to power applications that function with an electrolyzer, hydrogen storage, and release through recycled waste heat. A couple of highly developed companies in this space are GKN and MAHYTEC, who also works in compressed gas storage. (I will highlight an interesting project by GKN for utility scale storage later in this article).

Complex Hydrides: Complex hydrides are compounds that contain transition metal-hydrogen complexes in their structure and typically offer very high volumetric densities. The gravimetric density is also larger than that found in metal hydrides. However, the thermal dissociation of these compounds requires high (above 200C) temps and is not fully reversible. Some novel engineering designs such as is seen with Plasma Kinetics intriguing computer chip-like light activated wafer design are things to look out for.

Chemical: Finally, chemical hydrogen storage through chemicals like ammonia, has had a ton of traction recently. There is already a major push to utilize existing infrastructure in the ammonia space by first decarbonizing existing production and then utilizing it as an easier-to-handle hydrogen carrier. Ammonia, as an example, operates at a much lower pressure and easier temperature than Hydrogen, and has existing infrastructure, causing the cost to store and transport much lower. The main issues are the higher temperature needed for release of the hydrogen, and the complex dehydrogenation pathway, not to mention regulatory hurdles. To see some of the work that we have done in the ammonia space, check out our recent article on the topic, including a value chain framework. We will be continuing work in this space with an event later in the year.

SOLID-STATE STORAGE - New Developments

Earlier this year, we received an innovation concierge request for an overview of solid-state hydrogen storage methods, with the cited need case of avoiding some of the aforementioned issues with traditional physical storage. If you start digging into the pool of companies with offerings in the solid state hydrogen space, you’ll find that even those that are commercialized tend to stick to solutions with far less storage potential than needed by any utility applications. However, metal-hydride storage company GKN Hydrogen, with the benefit of their larger company group having years of experience in metal powders, sinter metals, and additives, has a commercialized technology, a decently developed supply chain that is steadily growing, and most exciting – a stackable solution at the MW scale. Recently announced was a project implementing this system between NREL and SoCalGas, which will involve an electrolyzer and a fuel cell (as in their integrated smaller scale systems), to produce green hydrogen from renewable sources, store it, then convert it back to renewable electricity. A recent press release contained a quote from Neil Navin, VP of clean energy innovations at SoCalGas:

“SoCalGas will leverage the large-scale hydrogen storage capabilities of GKN’s HY2MEGA from this project to help accelerate the commercialization and deployment of green hydrogen projects. Ultimately, green hydrogen generation and storage will help decarbonize the energy system while assuring stability of the electrical grid to enable even higher penetrations of renewable sources of electricity.”

If you’re looking at a comparison between lithium-ion batteries, pressurized hydrogen, and metal hydrides for this scale of energy storage, it’s hard not to be at least intrigued. Not only does this form of storage reduce safety and regulatory concerns, it is fully recyclable, has a 20+ year lifespan, can potentially eliminate the need for additional compression depending on configuration, has a significantly smaller footprint than hydrogen stored as a gas, and has shown initial cycle testing of < 1% storage loss for over 3500 cycles, compared to ~12-25% loss per 500 cycles with traditional lithium-ion batteries. If you’d like to read more about the SoCalGas/GKN/NREL project, check out this recent partnership report on the Darcy Platform, and if you want to learn more about the potential for solid-state hydrogen storage, come to our upcoming Hydrogen Storage and Transport series event on August 9.

Finally, we want to hear from you! Are you interested in solid state hydrogen storage?

Comment below or send an email to lindseym@darcypartners.com and let us know your thoughts!